In the process of manufacturing a semiconductor device, the introduction of impurities (dopant) is a step required for forming a p-n junction in a semiconductor wafer. Currently, impurities are generally introduced by ion implantation and subsequent annealing. Ion implantation is a technique of ionizing elements of impurities such as boron (B), arsenic (As), or phosphorous (P) to collide the ions with a silicon semiconductor substrate at high acceleration voltage, thereby physically implanting impurities (for example, see Patent Document 1). The implanted impurities are activated through annealing.
Traditionally performed ion implantation has an advantage of easily controlling the implantation depth and concentration of impurities in the introduction of impurities. The increasingly smaller sizes of semiconductor devices, however, require the introduction of impurities in only an extremely shallow region (with a depth not greater than several nm) of a surface layer of the substrate. Ion implantation has difficulty in accurately implanting impurities in only such an extremely shallow surface layer region. The 3D transistor technology, which has been under development, needs to introduce impurities into a concavo-convex three-dimensional pattern. It is therefore difficult to introduce impurities uniformly into the entire surface of the concavo-convex pattern by ion implantation of colliding ions from one direction.
Under the circumstances, the following technique has been researched, which forms a dopant-containing monolayer on the surface of a silicon substrate by a wet treatment and diffuses the dopant in a substrate surface layer by a subsequent heat treatment, thereby introducing impurities into only an extremely shallow region of the substrate surface layer (see Non-Patent Document 1). The dopant diffusion from a monolayer allows the introduction of impurities into only an extremely shallow region of a substrate surface layer. Additionally, forming a dopant-containing monolayer by a wet treatment allows impurities to be uniformly introduced into an entire surface having a complex concavo-convex pattern.